This invention relates to a coupling used with an automatic connecting and disconnecting device for hydraulic and pneumatic pipings for general industrial machinery, such as disclosed in Japanese patent publication No. S51-41934.
Japanese patent opening gazette No. S64-43292 discloses a pipe coupling of this type as described below with reference to FIGS. 1 and 2 of the accompanying drawings. This coupling comprises a first main body 2 fixed to a stationary face plate 1 and a second main body 4 fixed to a movable face plate 3. The first main body 2 is cylindrical in shape and has a joint mouth 5 in the front face and a pipe joint at the rear end. The second main body 4 has a front end portion having an outer diameter fitting in the joint mouth 5 and includes a second valve hole 8 in its front face 7 and a pipe joint 9 at the rear end. The first and second main bodies 2 and 4 have a common axis when they are fixed to the respective face plates 1 and 3 and the second main body 4 is adapted to move along the axis with movement of the movable face plate 3. The first main body 2 encloses therein a valve seat 10 sliding freely along the same axis. A valve seat 10 disposed in the first main body 2 can freely slide along the same axis. The valve seat 10 has a first valve hole 11 in its front end wall and is urged by a first spring 12 towards the joint mouth 5 to butt against a step 13 of the first main body 2. The first valve hole 11 is provided with a first check valve 14 for closing the valve hole 11 from its outside. The first main body 2 also encloses separately therein a valve hole 15 and a check valve 17 which is urged forward by a spring 16 to close the check valve 17 and the check valve 17 is coupled with the first check valve 14 through a connecting rod 18. The second main body 4 encloses therein a second check valve 20 having a greater diameter than the first check valve 14, which is urged by a second spring 19 for closing the second valve hole 8 from its inside. An annular sealing member 21 is disposed on the front face of the valve seal 10 at a position facing the front face of the second main body 4. The sealing member 21 is adapted to enclose the first and second valve holes 11 and 8 when the front face 7 is put into contact with the front face of the valve seat 10, so that, in such connected state, the valve seat 10 is urged against the second main body 4 to keep a sealed state by a hydraulic pressure acting to the valve seat 10 due to the diameter difference between the valve seat 10 and the sealing member 21.
This pipe coupling can be put into a connected state of FIG. 2 from a disconnected state of FIG. 1 by moving the movable face plate 3 toward the stationary face plate 1 by a predetermined distance. More specifically, when the second main body 4 fits in the joint mouth 5 of the first main body 2, the front face 7 of the second main body 2 is put in contact with the front face of the valve seat 10. With further movement, the front face of the second check valve 20 is put in contact with the front face of the first check valve 14 and the valve seat 10 is moved backward in the second main body 2 against the first spring 12 to cause the first check valve 14 to open the first valve hole 11. At the same time, the check valve 17 and the second check valve 20 push one another through the connecting rod 18 to open the valve hole 15 and the second valve hole 8, thereby providing a passageway between the pipe joints 6 and 9.
If the movable face plate 3 is moved backward from the state as shown in FIG. 4, a motion opposite to the above takes place. More specifically, the second check valve 20 and the check valve 17 are closed and, thereafter, the first check valve 14 is closed. Then, the valve seat 10 is moved forward in the first main body 2 and the front face 7 of the second main body 4 leaves the front face of the valve seat 10 to come in the disconnected state as shown in FIG. 1.
The above-mentioned prior art coupling shows no particular problem when any fluid is let flow therethrough after interrupting the feed of fluid into the first and second main bodies and then putting the coupling into the connected state of FIG. 2 from the state of FIG. 1. When both main bodies are connected under such a condition that high pressure fluid is kept in the second main body 4, however, the valve seat 10 may be separated from the second main body 4 by the fluid pressure during the connecting process to cause a problem of fluid leakage.
A cause of this fluid leakage is in the diameter difference provided between the second valve hole 8 of the second main body 4 and the annular sealing member 21. This diameter difference is resulted necessarily from the fact that the annular sealing member 21 is adapted to face a predetermined width of the annular front face 7 of the second main body 4, which encloses the second valve hole 8, at an intermediate position of the width. When the second check valve 20 slightly leaves the second valve hole 8 in the process from the state of FIG. 1 to the state of FIG. 2, therefore, the high pressure fluid in the second main body 4 flows out therethrough and into part of the gap between the front face 7 of the second main body 7 and the front face of the valve seat 10, which is inside the annular sealing member 21. At this time, however, the first valve hole 11 is not yet open enough and, therefore, the valve seat 10 is moved backward by the fluid pressure to cause temporary fluid leakage. When a high fluid pressure acts in the first main body 2, no fluid leakage will occur since the valve seat 10 is urged forward by this fluid pressure.